57 research outputs found
Artificial Gauge Field and Quantum Spin Hall States in a Conventional Two-dimensional Electron Gas
Based on the Born-Oppemheimer approximation, we divide total electron
Hamiltonian in a spinorbit coupled system into slow orbital motion and fast
interband transition process. We find that the fast motion induces a gauge
field on slow orbital motion, perpendicular to electron momentum, inducing a
topological phase. From this general designing principle, we present a theory
for generating artificial gauge field and topological phase in a conventional
two-dimensional electron gas embedded in parabolically graded
GaAs/InGaAs/GaAs quantum wells with antidot lattices. By tuning
the etching depth and period of antidot lattices, the band folding caused by
superimposed potential leads to formation of minibands and band inversions
between the neighboring subbands. The intersubband spin-orbit interaction opens
considerably large nontrivial minigaps and leads to many pairs of helical edge
states in these gaps.Comment: 9 pages and 4 figure
No-Reference Light Field Image Quality Assessment Based on Micro-Lens Image
Light field image quality assessment (LF-IQA) plays a significant role due to
its guidance to Light Field (LF) contents acquisition, processing and
application. The LF can be represented as 4-D signal, and its quality depends
on both angular consistency and spatial quality. However, few existing LF-IQA
methods concentrate on effects caused by angular inconsistency. Especially,
no-reference methods lack effective utilization of 2-D angular information. In
this paper, we focus on measuring the 2-D angular consistency for LF-IQA. The
Micro-Lens Image (MLI) refers to the angular domain of the LF image, which can
simultaneously record the angular information in both horizontal and vertical
directions. Since the MLI contains 2-D angular information, we propose a
No-Reference Light Field image Quality assessment model based on MLI (LF-QMLI).
Specifically, we first utilize Global Entropy Distribution (GED) and Uniform
Local Binary Pattern descriptor (ULBP) to extract features from the MLI, and
then pool them together to measure angular consistency. In addition, the
information entropy of Sub-Aperture Image (SAI) is adopted to measure spatial
quality. Extensive experimental results show that LF-QMLI achieves the
state-of-the-art performance
In Situ Construction of an Ultrarobust and Lithiophilic Li-Enriched LiâN Nanoshield for High-Performance Ge-Based Anode Materials
Alloy-based materials are promising anodes for rechargeable batteries because of their higher theoretical capacities in comparison to graphite. Unfortunately, the huge volume changes during cycling cause serious structural degradation and undesired parasitic reactions with electrolytes, resulting in fragile solid-electrolyte interphase formation and serious capacity decay. This work proposes to mitigate the volume changes and suppress the interfacial reactivity of Ge anodes without sacrificing the interfacial Li+ transport, through in situ construction of an ultrarobust and lithiophilic Li-enriched LiâN nanoshield, which demonstrated improved chemical, electrochemical, mechanical, and environmental stability. Therefore, it can serve as a versatile interlayer to facilitate Li+ transport and effectively block the attack of electrolyte solvents, thus boosting the long-term cycle stability and fast charging capability of Ge anodes. This work offers an alternative methodology to tune the interfaces of other electrode materials as well by screening for more N-containing compounds that can react with Li+ during battery operation
Boosting Superior Lithium Storage Performance of AlloyâBased Anode Materials via Ultraconformal Sb CoatingâDerived Favorable SolidâElectrolyte Interphase
Alloy materials such as Si and Ge are attractive as highâcapacity anodes for rechargeable batteries, but such anodes undergo severe capacity degradation during dischargeâcharge processes. Compared to the overâemphasized efforts on the electrode structure design to mitigate the volume changes, understanding and engineering of the solidâelectrolyte interphase (SEI) are significantly lacking. This work demonstrates that modifying the surface of alloyâbased anode materials by building an ultraconformal layer of Sb can significantly enhance their structural and interfacial stability during cycling. Combined experimental and theoretical studies consistently reveal that the ultraconformal Sb layer is dynamically converted to Li3Sb during cycling, which can selectively adsorb and catalytically decompose electrolyte additives to form a robust, thin, and dense LiFâdominated SEI, and simultaneously restrain the decomposition of electrolyte solvents. Hence, the Sbâcoated porous Ge electrode delivers much higher initial Coulombic efficiency of 85% and higher reversible capacity of 1046 mAh gâ1 after 200 cycles at 500 mA gâ1, compared to only 72% and 170 mAh gâ1 for bare porous Ge. The present finding has indicated that tailoring surface structures of electrode materials is an appealing approach to construct a robust SEI and achieve longâterm cycling stability for alloyâbased anode materials
Tensor oriented no-reference light field image quality assessment
Light field image (LFI) quality assessment is becoming more and more important, which helps to better guide the acquisition, processing and application of immersive media. However, due to the inherent high dimensional characteristics of LFI, the LFI quality assessment turns into a multi-dimensional problem that requires consideration of the quality degradation in both spatial and angular dimensions. Therefore, we propose a novel Tensor oriented No-reference Light Field image Quality evaluator (Tensor-NLFQ) based on tensor theory. Specifically, since the LFI is regarded as a low-rank 4D tensor, the principal components of four oriented sub-aperture view stacks are obtained via Tucker decomposition. Then, the Principal Component Spatial Characteristic (PCSC) is designed to measure the spatial-dimensional quality of LFI considering its global naturalness and local frequency properties. Finally, the Tensor Angular Variation Index (TAVI) is proposed to measure angular consistency quality by analyzing the structural similarity distribution between the first principal component and each view in the view stack. Extensive experimental results on four publicly available LFI quality databases demonstrate that the proposed Tensor-NLFQ model outperforms state-of-the-art 2D, 3D, multi-view, and LFI quality assessment algorithms
Perceptual evaluation of light field image
Recently, light field image has attracted wide attention. However, much less work has been conducted on the perceptual evaluation of light field image. In this work, we create the first windowed 5 degree of freedom light field image database (Win5-LID) based on stereoscopic display, which provides windowed 5 DOF experience and all the depth cues of light field image. The database consists of light field images with representative compression and reconstruction artifacts. We assume that the light field quality is not only affected by sub-views quality but also depth cues. Picture quality and overall quality are then evaluated and the results validate our assumption. Finally, the performance of existing image quality metrics is analyzed on our database. The results indicate that the performance of the state-of-the-art image quality metrics remains to be improved
No-reference light field image quality assessment based on spatial-angular measurement
Light field image quality assessment (LFI-QA) is a significant and challenging research problem. It helps to better guide light field acquisition, processing and applications. However, only a few objective models have been proposed and none of them completely consider intrinsic factors affecting the LFI quality. In this paper, we propose a No-Reference Light Field image Quality Assessment (NR-LFQA) scheme, where the main idea is to quantify the LFI quality degradation through evaluating the spatial quality and angular consistency. We first measure the spatial quality deterioration by capturing the naturalness distribution of the light field cyclopean image array, which is formed when human observes the LFI. Then, as a transformed representation of LFI, the Epipolar Plane Image (EPI) contains the slopes of lines and involves the angular information. Therefore, EPI is utilized to extract the global and local features from LFI to measure angular consistency degradation. Specifically, the distribution of gradient direction map of EPI is proposed to measure the global angular consistency distortion in the LFI. We further propose the weighted local binary pattern to capture the characteristics of local angular consistency degradation. Extensive experimental results on four publicly available LFI quality datasets demonstrate that the proposed method outperforms state-of-the-art 2D, 3D, multi-view, and LFI quality assessment algorithms
Metabolic network as an objective biomarker in monitoring deep brain stimulation for Parkinson's disease: a longitudinal study.
BACKGROUND
With the advance of subthalamic nucleus (STN) deep brain stimulation (DBS) in the treatment of Parkinson's disease (PD), it is desired to identify objective criteria for the monitoring of the therapy outcome. This paper explores the feasibility of metabolic network derived from positron emission tomography (PET) with 18F-fluorodeoxyglucose in monitoring the STN DBS treatment for PD.
METHODS
Age-matched 33 PD patients, 33 healthy controls (HCs), 9 PD patients with bilateral DBS surgery and 9 controls underwent 18F-FDG PET scans. The DBS patients were followed longitudinally to investigate the alternations of the PD-related metabolic covariance pattern (PDRP) expressions.
RESULTS
The PDRP expression was abnormally elevated in PD patients compared with HCs (Pâ<â0.001). For DBS patients, a significant decrease in the Unified Parkinson's Disease Rating Scale (UPDRS, Pâ=â0.001) and PDRP expression (Pâ=â0.004) was observed 3Â months after STN DBS treatment, while a rollback was observed in both UPDRS and PDRP expressions (both Pâ<â0.01) 12Â months after treatment. The changes in PDRP expression mediated by STN DBS were generally in line with UPDRS improvement. The graphical network analysis shows increased connections at 3Â months and a return at 12Â months confirmed by small-worldness coefficient.
CONCLUSIONS
The preliminary results demonstrate the potential of metabolic network expression as complimentary objective biomarker for the assessment and monitoring of STN DBS treatment in PD patients. Clinical Trial Registration ChiCTR-DOC-16008645. http://www.chictr.org.cn/showproj.aspx?proj=13865
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